Look on your desktop. Do you see a folder
called; '''Old Firefox?''' Look inside.
Look for the folder with the latest creation date.
https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

Type about:profiles<enter> in the address bar.
How many profiles are listed?
How many should be there?
Also, open the profile folder in your file explorer.

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible
http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder
https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
Type '''about:profiles'''<enter> in the address bar.
How many profiles are listed?
How many should be there?
Also, open the profile folder in your file explorer.